Transcript populations - Doral Academy Preparatory

POPULATIONS
CHAPTER 19
POPULATIONS
Population-all
of the individuals of a
species that live together in one
place at one time.
Demography-the statistical study of
populations. It is used to predict how
the size of a population will change.
KEY FEATURES OF
POPULATIONS
1.
Population size
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– is the number of individuals in a population.
– has an important effect on the ability of the
population to survive.
A small population is more likely to become extinct:
 -in the case of random events or natural disaster
 -due to inbreeding where the population is more
genetically alike. Recessive traits are more likely
to appear.
 -with reduced variability it is harder to adapt to
changes.
KEY FEATURES OF
POPULATIONS, con’t
2. Population density
 – the number of individuals in a given area.
 – if they are too far apart they may only rarely
encounter one another resulting in little
reproduction.
KEY FEATURES OF POPULATIONS, con’t
Population size is limited by:
density-dependent factors
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density-independent factors
Disease
Competition
Predators
Parasites
Food
Crowding
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The greater the population,
the greater effect these
factors have.
Ex. Black plague in the
Middle Ages – more deaths
in cities
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Volcanic eruptions
Temperature
Storms
Floods
Drought
Chemical pesticides
Major habitat disruption (as
in the New Orleans
flooding)
Most are abiotic factors
KEY FEATURES OF
POPULATIONS, con’t
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3. Dispersion
– the way in which the individuals are
arranged.
Mostcommon
PREDICTING POPULATION
GROWTH
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Model:
A hypothetical population that has key
characteristics of the real population being
studied.
Used by demographers to predict how a
population will grow.
PREDICTING POPULATION
GROWTH, con’t
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Nearly all populations will tend to grow
exponentially as long as there are
resources available.
Two of the most basic factors that affect
the rate of population growth are the birth
rate, and the death rate.
r(rate of growth)=birth rate – death rate
PREDICTING POPULATION
GROWTH, con’t
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Exponential growth curve:
population growth plotted
against time.
As a population gets larger,
it also grows at a faster rate.
This is the maximum
population growth under
ideal circumstances.
Includes plenty of room for
each member, unlimited
resources (food, water) and
no hindrances (predators).
FACT: No population exhibits this type of growth for long.
PREDICTING POPULATION GROWTH, con’t
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Logistic model: This model accounts for the
declining resources available to populations as
they grow.
It assumes the birth and death rates are not
constant.
As the population grows, births decline and
death rises.
Eventually birth=death so the population stops
growing.
Carrying capacity (K): The number of organisms
of one species that an environment can support
indefinitely.
PREDICTING POPULATION GROWTH, con’t
Two modes of population growth.
The Exponential curve (also known as a Jcurve) occurs when there is no limit to
population size.
The Logistic curve (also known as an S-curve)
shows the effect of a limiting factor (in this case
the carrying capacity of the environment).